Let p denote an odd prime. The
following three identities (transformation formulae) involving the Legendre symbol
() are known to be valid for any complex-valued function F defined on the integers,
which is periodic with period p:
∑x=0p−1F(x)
+∑x=0p−1()F(x)
=∑x=0p−1F(x2),
∑x=0p−1F(x)
+∑x=0p−1()F(x)
=∑x=1p−1F(x +),a≢0(modp),
∑x=0p−1F(x)
+∑x=0p−1()F(x)
=∑x=1p−1F(x + 2 +).
We consider a general class of transformation formulae, which includes the above
examples.